The invention relates to a method for checking data sequences, comprising a protection step and a verification step, with a control sequence being formed in the protection step on the basis of an identification sequence, which identification sequence comprises identification values which identify the data sequences which are to be protected, and which control sequence comprises control values of which at least some have been formed on the basis of operation values, which operation values have been derived from data of sequences which were identified by the said identification values, and with the data sequences being verified, in the verification step, on the basis of the control values. Such a method is known in practise.
Identification values are used in such known methods to form operation values on the basis of data of corresponding sequences. In this context the sequences can for example be files, whereas the identification values can be the names or "identifiers" of said files. The operation values, which can for example be so-called hash values, can be incorporated as such or after a further operation (processing) into the control sequences (control file). In this context the control sequence (or verification sequence) acts as an addition to the data sequences. By comparing the values in the control sequence to values, which are directly obtained from the data sequences by carrying out a suitable operation, the integrity of the data sequences concerned can be checked.
In that context, however, it is also possible that third parties having at their disposal both the sequences themselves and the control file, can introduce changes in the sequences in a relatively simple manner if they can include said changes into the control file, since the control sequence (control file) comprises, with prior art methods, both the control values and the identification values. If the operation concerned is known, after all, a third party can also implement said operation and thus alter the control sequence, as a result of which alterations remain invisible. Furthermore, while both transferring identification values and control values, a relatively large amount of data has to be incorporated into the control sequence. Moreover, checking the sequences, with the prior art methods, takes a relatively large amount of time as the verification step has to be implemented each time for all data sequences with all the identification values and control values.